Electric Launch Design optimized for semi-displacement speeds

Today's test with EcoSmart 83 with electric powertrain.

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Thank you, Jurgen - would love it if you could say more about this graph. I take it R/W is empirical total resistance over total weight as tested? Is volumetric Froude number then also based on total weight as tested, or is it based on a different datum displacement?

Is the gray line the test data?
What's the red line?

 

Total weight is the base in all my test.
JS

 

https://www.roundbritain-erib.org/

 

We're in the new issue of Professional BoatBuilder, as the "Parting Shot" on the last page.
https://digital.emagazines.com/professional_boatbuilder/20240716/index.html
Please regard as final the SOP as it appears in Professional Boatbuilder and below as post #126. The discussion of which electric motor may be taken as suggestive rather than limiting.

We are proceeding as a design contest, with the final deadline being in May 2025 (at the end of college's academic year), with contestants encouraged to submit entries well before that so a committee of vetting judges, chaired by our very own TANSL, can provide support and feedback to give each contestant a fair shot ant having their hull forwarded to Perry Van Oossanen for evaluation.

TANSL has indicated he is interested in allowing a measure of design freedom, so if you are inclined to submit a boat outside the "box" defined by the SOP, run that by TANSL - he'll be receptive and ready to assist.

As organizer I hope to have final say over the SOP and the end objective. The objective, subject to approval by participating others, is to graph multiple designs and their variants thus:

On the graph above, L = Waterline Length.

Please seek to minimize the area under the resistance curve between length Froude Numbers .o5 and .08 (assume resistance will be calculated at 0.1 increments and that the trapezoidal rule will be used) consistent with achieving an ISO 12217 Crew Limit (CL) of minimum 8, preferably 9, on a 26 foot waterline while achieving a 70 nautical mile range using electric power alone as stipulated in the SOP.

An aside concerning nomenclature: I see lFn=0.4 to 0.5 and lFn=0.8 to 0.9 as transition zones that sometimes go by the names "Fast Displacement" for 0.4 to 0.5 and "Semi-Planing" for 0.8 to 0.9. It may be that volumetric Froude number makes sense for speeds above lFn=0.8, but below 0.8 I don't think so and neither did Stevens Institute researcher Daniel Savitsky.

While I have been unable to locate a copy of Robert Beebe's Voyaging Under Power to confirm, the form of the graph above is consistent with my recollection of graphs in that book.

 

Electric Launch Design optimized for semi-displacement speeds
Final SOP, as published in the August / September issue of Professional BoatBuilder

Intent: A multi-purpose electric launch,
comparable in utility to an Oldport 26.

Purpose: Support for a yacht club or
marina that emphasizes sailing and where
most boats are kept on moorings in the
northern summer season. Launches will be
expected to serve as committee boat, photo
boat, instructor/coach, and tow boat for
youth and dinghy programs, to run errands
on the other side of a bay, and to occasion-
ally make a short transit across unprotected
ocean. The yacht club has slips available
with shore-power hookups; Tesla-style
chargers could be adapted. The club does
not have a conventional fuel dock.

In the winter season the launch might be
taken aboard a superyacht or cruise ship
headed for the Caribbean to transport people
ship-to-shore. The hypothetical mothership
utilizes an alternative fuel and deliberately
does not carry conventional gasoline or diesel.
Using the alternative fuel, it has significant
onboard electric-generating capacity.

Length limit: 8m (26' ) waterline

Capacity: Submitting designers are asked
to target an ISO 12217 Category C “crew limit”
of 9 (8 passengers and one operator).
If the target is missed by one, and the
Category C CL ends up being 8, that is acceptable.
In all cases, stability calculations and
tests will assume a human payload of 700
kg (1,540 lbs). Resistance calculations
will be run at 3⁄4 load: 525 kg (1,157.43 lbs).
(This may be modified in certain instances
at the discretion of the judges.)

The half-load condition may be used to calculate range.

Intended top speed with two people and gear of combined weight 380 lbs (172 kg): 15.3 knots (28.3 km/h or 7.87 m/s).

Intended top speed, 3⁄4 load (525 kg): 13.6 knots (25.2 km/h or 7.00 m/s).

Intended cruise speed, all load conditions: 11.9 knots (22.0 km/h/ or 6.12 m/s)

Proposed power: Pure Watercraft 25-kW electric outboard system or Elco 50 hp
(either outboard or inboard). Torqeedo Deep Blue, ePropulsion, or Flux Marine units could be utilized if one of their size offerings is deemed appropriate by the designer. Equivalent inboards would be fine as well.

Suggestions for twin installations: Torqeedo Cruise 10.0 or 12.0 outboards, ZeroJet 18-kW outboards or equivalent twin inboards. Elco, ePropulsion, or Flux Marine units could be considered if a pair of such units is deemed appropriate by the designer.

Mounting one or more outboards forward in a well, converting a Pure Watercraft unit to an azimuthing pod drive, or other innovations are encouraged.
Jet drives are not prohibited, but the conventional wisdom is that most current models are not efficient at the intended speeds, so calculations showing
otherwise would need to be included. Discussion of self-pitching props is welcome.

Proposed battery and power system:
TBD.

Note that Pure Watercraft builds a
pontoon-boat-style catamaran with single or
twin 25 kW outboards. That boat shares a
battery and power system with the Chevy
Bolt EV with the following specs:

• 12V auxiliary power up to 10 amps for onboard electronics.
• 65-kWh automotive battery pack from GM.
• Integrated level I & II Charger supporting 120V/240V charging.
• Support for DC Fast Charging.
​

Range: 70 nautical miles in 8 hours or less in the half-load condition (weight of persons on board: 350 kg (772 lbs)).

Scratch boat: The Uffa Fox design Ankle Deep (http://www.uffafox.com/ankledp.htm), scaled up
slightly to a 26' waterline length.

 

What are you willing to pay for the boat you are describing?
JS

 

I'm potentially interested in a business stake in the company that builds it, ideally in partnership with an electric motor company. I know of specific marina / dealerships that would very much like to carry an up-to-date, quality line of launches. My "Parting Shot" is not the only article in the August / September 2024 Professional BoatBuilder concerned with launches and their variants.

If you'd like for me to make US marina / dealerships aware of your current electric model, Jurgen, I might be interested in doing that. At the moment, though, my main interest is in comparing candidate designs - your work and that of Nigel Irens', for instance - and in involving younger designers in moving the state-of-the-art forward. My current design is a front-facing rowboat, and my current personal shopping is for a (possibly live-aboard) sailboat and possibly a drone with which to video the rowboat.

 

What on earth does that mean?
And define - state of the art?

 

Here's the best way to do that. It's a battery energy storage system (battery ESS)—centered view of the best way to lower carbon or GHG emissions constructively and responsibly. There is no way to deploy batteries on a boat that is even close to deploying batteries in an energy storage system on land.

Here are some battery storage basics. Batteries only make sense for storing energy for periods of 16 hours or less (that's the best tech available and expected for the next decade). You need to cycle the rated capacity through the battery every day, 365 days per year, for about 10 years, to get the cost of storage down to about 5.1 cents per kWh. All ESS batteries need to be deployed with that cost point as a target. Note that many electrical utility Time Of Use (TOU) billing schedules have a 5-6 cent peak-rate margin over the off-peak rate.

So what you do is set up a hybrid grid tie PV solar system with ESS. Use the battery ESS to offset consumption during peak hours 365 days a year. Use the savings to buy jug gas for an outboard-powered boat. This will be cheaper, and far more effective wrt GHG and carbon, than trying to use batteries on the boat. The entire hybrid grid-tie PV and ESS will cost about what the boat's dock-side equipment charging system would cost (30K US). Unlike the dock-side equipment, The PV system pays for itself; and you get the same ESS throughput with maybe 1/3 the batteries and 1/3 the cost. The vessel will weigh 1.5 tons less with an outboard than with batteries, will have greater versatility, and will consume far less energy in use.

So do the following - measure the annual fuel consumption and the total logistic cost of the boat's fuel provision. Compute the size of solar PV system that will yield a net offset of the GHG and carbon emissions of the marina skiff.

The simple fact is that energy density is king for transport durations over a few minutes. The weight of the batteries on a 26' boat will quickly produce the situation where half the batteries are there solely to propel the batteries. The other simple fact is that it is very expensive to store energy in a battery. It costs a minimum of 5.1 cents per day per kWh because batteries age out (and that's a grid-scale system figure, you can probably double that for a small boat system). The consensus is that this will decrease by 1% in real costs per year for the next ten years, so it basically a fixed cost; and the economic crossover for storage duration isn't going to exceed 17 hours in the next ten years. Fuel tanks also age out, but with a much lower daily cost per stored kWh. So storing energy for more than 16 hours should not be done with batteries, but with gas or diesel.

 

As far as the boat goes, the proposals for the propulsions system should include an analysis of the battery's thermal management and fire suppression system. We still don't have an inherently safe or self-extinguishing high performance battery, so third party thermal management and fire extinguishing must be chosen and integrated by the vessel designer. Assessing the weight and space requirements of these systems is also important. Water-based fire suppressants that boil off and leave an encapsulating film behind to block oxygen are looking good, but are still experimental; and they will probably end up decreasing specific energy and energy density by about 25%. Processing the cell cans to be able to live in an aqueous bath for thirty years isn't trivial either.

Fire resistant lithium battery experiment - Lithium-Ion Batteries (LIBs) Immersed in Fire Prevention Material for Fire Safety and Heat Management https://www.mdpi.com/1996-1073/17/10/2418
Last week's e-boat fire in Austria -

 

Involving younger designers means project-based learning for interested engineering / naval architecture students and other interested parties. As for defining the current state-of-the-art I'm leaving that to Perry Van Oossanen, whose father wrote at least one of the previously recommended papers. The aim is to minimize the area under the resistance curve at lFn 0.5-0.8 while meeting ISO criteria and utilization objectives per my post #125.

Van Oossanen designs for Heesen Yachts, among others. HullVane is an afilliated company.

 

PhilSweet: I personally witnessed a gasoline fire aboard a classic powerboat at Mystic Seaport during (but the boat was not part of) the WoodenBoat Show a month ago.

Quoting Nigel Calder from Pushing batteries to the limit - Ocean Navigator https://oceannavigator.com/pushing-batteries-to-the-limit/

Two chemistries predominate in the marine lithium-ion world: lithium iron phosphate (LFP), and nickel manganese cobalt (NMC). If LFP is driven into thermal runaway, it will not generate high enough temperatures to set itself on fire, whereas NMC can. For this reason, LFP has often been described as intrinsically safe and has been promoted as the only suitable chemistry for marine applications. However, as noted above, the electrolyte is still flammable and there have been some notable fires and boat losses.

Within the LFP and NMC families, there are literally dozens of variations in terms of construction, chemical doping, protective measures, etc. Given the correct BMS and packaging, it is arguable that NMC can be made as safe as LFP; there are certainly some NMC batteries that are safer than some LFP batteries. Regardless of chemistry, the only lithium-ion batteries that I will consider putting in my boat must have been subjected to rigorous third-party abuse testing to a recognized standard (notably Underwriters Laboratories UL 1973) and/or come from a respected marine brand with a significant lithium-ion track record.​

There are also new types entering the market, such as:

• Silicon in place of carbon: Sila | Next-Gen Lithium-Ion Battery Materials https://www.silanano.com/
• Solid state batteries that utilize sodium and aluminum rather than lithium and copper
• Other chemistries

My view is that it's up to the motor / power package company rather than the hull designer to get these things right. Having said that, a thorough discussion of choices made is to be encouraged. Thank you for adding your thoughts.

On the weight side I'm not averse to swappable batteries if the time it takes to change them out is included in the 8 hours allotted to cover 70 miles. It's very typical on job sites to have two batteries going for each drill/screwdriver in use. For boats I suppose a davit at the shoreside charging station would be employed.

 

May I ask you a question, AdHoc? What would you like to contribute to defining "state of the art"? Or maybe you would change the term to "fully up-to date" or "fully modern"?

Would you agree that this is a video of a "fully modern" electric boat design?


What if the hydrofoils were optional? What if the intent were to design a single hull for use with or without hydrofoils, with the base model being the simple one: without. Would we change anything, or simply adopt or adapt an old model like the Oldport 26?

In the process, if we were to come up with a hull design improvement for 26' waterline launches, might it influence the design of vessels such as NEW BUILD - 42m Crew Supply Vessel - Kitset - SeaBoats https://www.seaboats.net/new-build-42m-crew-supply-vessel-kitset-676499?

 

TANSL: This looks like potentially useful and inexpensive software (though there's a restriction for EU users about paying their own VAT). Should we recommend its use to contest entrants? Displacement and Semi-Displacement (or Semi-Planing) Hull Powering Calculations, Description https://hawaii-marine.com/templates/Products/Pwr-Disp/description.htm